The present invention relates to a connection between a circuit and a discrete electrical component, and more particularly, to a connection for carrying a high frequency signal between a circuit and a discrete electrical component.
Technology for radio-frequency (RF) communications is developing at a very rapid pace. When the cellular telephone industry developed, for example, the telephones operated in the relatively low frequency range of 800 MHz to 900 MHz. Early cellular telephones and RF communication devices were also very large and bulky.
Communications technology has made great strides since these original cellular phone were developed and marketed. One improvement is the development of communication equipment that transmits at much higher frequencies, which has many advantages. One advantage of transmitting at high frequency is that the communication equipment can be made much smaller and cost effective.
Another advantage is that a high frequency signal can carry more information than a low frequency signal. This advantage is very important as both our society and economy become more dependent on information. Furthermore, communication devices are being used more and more to communicate data in addition to voice information. Examples of such devices that need to communicate massive amounts of data include cellular phones that provide wireless Internet access, wireless modems, and wireless network connections.
While high frequency RF communication has such strong advantages, there are some practical limitations to the ability to design circuitry that can effectively process an RF signal. One of the problems is that some portions of the signal path in many of the circuits are too long relative to the wavelength of the signal that is propagating along the path, which causes an excessive amount of degradation in the signal. For example, many electrical circuits and components are mounted on a wafer and cut into a die. The contact point or pad is usually on a top portion of the die. Additionally, the input and output of these signals are filtered through a capacitor that is mounted on the circuit board adjacent to the die. A wire is then positioned between a contact point or pad on top of the die and a trace or signal path printed on the circuit board.
However, the length of the wire required to reach from the top of the die to the trace on the surface of the circuit board is too long for very high frequency signals, especially those signals that have a frequency above 20 GHz. One phenomenon that results in degradation of such a signal is the impedance of the wire, which results in an inductance that opposes the flow of electrical current. If the wire is too long, the inductance is too great and results in signal loss and noise.
This problem is especially acute in dies that are relatively thick such as dies formed with silicon germanium (SiGe), which is otherwise advantageous because it is a very economical material to use when forming dies. Dies formed with SiGe are much thicker than those formed with gallium arsenide (GaAs), which is currently a more common material for forming dies. For example, the thickness of a SiGe die is about 10 mils and the thickness of a GaAs die is only about 2.5 mils. This extra thickness results in longer wires between the die and circuit board and thus more signal loss and noise in high frequency signals. Furthermore, because of the manufacturing process of building circuits, the wire gradually slopes down to the trace on the circuit board. Hence the wire becomes analogous to the hypotenuse of a triangle and has a length even longer than the depth of the die, which compounds the problem even more.
There are have been many different techniques to manufacture circuit boards that address these problems and either eliminate or minimize the length of the wire. One technique is to flip the die upside down to form a flip chip. The contact point of the die is then placed in direct electrical contact with the trace printed on the circuit board. Another technique is to have a recess or channel formed in the circuit board. The die is then mounted in the recess so that the top of the die is at about the same level as the trace printed on the circuit board.
However, all of these techniques introduce a new set of problems. For example, the flip chips are expensive to manufacture because of the difficulty in making a good solder contact point with the trace. Another problem with flip chips is that the dielectric characteristics of the circuit board will change the performance of the circuit or other electrical components mounted on the die. Using a circuit board that has channels is also very expensive to manufacture and thus is a poor choice for products that are price sensitive.
In general terms, the present invention relates to the communication of a high-frequency signal from a die or similar structure to a discrete electrical component. One advantage of this invention is that it enables translation of an electrical signal off of a die or similar structure with a reduced distribute inductance of the signal path and hence a reduced degradation of the signal.
One aspect of the present invention is an apparatus for processing high frequency signals. The apparatus comprises an electrical circuit having a top portion and a contact point positioned on the top portion. A discrete electrical component also has a top portion and a contact point positioned on the top portion. An intermediate signal path extends between the contact point on the top portion of the electrical circuit and the contact point on the top portion of the discrete electrical component.
An alternative aspect of the present invention comprises a circuit board having a trace. An electrical circuit is fabricated on a die, which is mounted on the circuit board. The die has a top portion and a contact point is positioned on the top portion. The circuit is configured to process a signal having a frequency in the range of about 20 GHz and higher. A capacitor is mounted on the circuit board and has a top portion and bottom portion. The bottom portion opposes the trace. A wire extends between the contact point on the top portion of the die and the top portion of the capacitor. The wire has a length in the range of about 2 mils to about 12 mils.
Another alternative aspect of the invention comprises a circuit board that includes an electrical circuit and a discrete electrical component. A wire extends between the electrical circuit and the discrete electrical component. The wire does not have direct contact with the circuit board.
Yet another aspect of the present invention is a method of manufacturing electronics, the electronics being mounted on a circuit board having a surface. The method comprises mounting an electrical circuit to the circuit board, the electrical circuit having a contact point elevated off the surface of the circuit board; mounting a discrete electrical component on the circuit board, the discrete electrical component having a contact point elevated off the surface of the circuit board; and positioning a conductive path between the contact of the electrical circuit and the discrete electrical component.
Still another aspect of the present invention is a method of processing a high frequency electrical signal. The method comprises conducting the electrical signal through an electrical circuit, the electric circuit being mounted on a circuit board, the electrical signal having a frequency in the range of about 20 GHz and higher; directly conducting the electrical signal from the electrical circuit to a signal path at a contact point physically isolated from the circuit board; and directly conducting the electrical signal from the signal path to a discrete electrical component at a contact point physically isolated from the circuit board.